1. Field of the Invention
The present invention relates to a method of producing an optical information recording medium in which information is recorded on the basis of a chemical change caused by laser beam irradiation.
2. Description of the Prior Art
Recently, vigorous research has been made on information recording by laser beam irradiation because the recording mentioned permits a very high recording density during actual time recording. A known optical information recording medium is produced by forming a thin calcogen film such as tellurium, a thin pigment film, etc. on a transparent resin substrate. However, a serious problem remains unsolved in the recording medium of this type. Specifically, the recording medium deteriorates during storage by the oxygen or water contained in the air or by the influence of ultraviolet light.
To overcome the defect noted above, a recording medium comprising a thin tellurium (Te) film containing carbon has been proposed in Japanese Patent Disclosure (Kokai)No. 57-165292. In this case, a Te target is sputtered by a hydrocarbon gas plasma so as to deposit on a substrate a Te layer containing the carbon separated from the hydrocarbon.
The sputtering technique is generally thought to utilize a plasma of rare gases such as argon gas as the sputtering gas. In other words, the use of a plasma gas highly reactive with the target metal or a decomposable gas such as hydrocarbon gas as in the Japanese Specification quoted previously is quite exceptional in its sputtering technique. In the case of using a decomposable gas, the decomposing process of the gas is greatly influenced by the power applied for generating a plasma from the decomposable gas, the plasma gas pressure in the step of forming a metal film, and the flow rate of the decomposable gas in the step of introducing the gas into the plasma-generating region, leading to marked changes in the characteristics of the resultant recording film. In addition, the conditions for forming a recording film depend on the type of sputtering apparatus used. It follows that it is necessary to conduct experiments many times in order to determine the optimum film-forming conditions for each sputtering apparatus.